81681688 has 32 divisors (see below), whose sum is σ = 167454720. Its totient is φ = 37044000.

The previous prime is 81681679. The next prime is 81681689. The reversal of 81681688 is 88618618.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81681689) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 54793 + ... + 56263.

It is an arithmetic number, because the mean of its divisors is an integer number (5232960).

Almost surely, 2^81681688 is an apocalyptic number.

81681688 is a gapful number since it is divisible by the number (88) formed by its first and last digit.

It is an amenable number.

81681688 is an abundant number, since it is smaller than the sum of its proper divisors (85773032).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81681688 is a wasteful number, since it uses less digits than its factorization.

81681688 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2119 (or 2115 counting only the distinct ones).

The product of its digits is 147456, while the sum is 46.

The square root of 81681688 is about 9037.7922082774. The cubic root of 81681688 is about 433.8852648916.

It can be divided in two parts, 81681 and 688, that added together give a square (82369 = 287²).

The spelling of 81681688 in words is "eighty-one million, six hundred eighty-one thousand, six hundred eighty-eight".